Determination of gap symmetry from angle-dependent H(c2) measurements on CeCu₂Si₂

Phys Rev Lett. 2011 May 20;106(20):207001. doi: 10.1103/PhysRevLett.106.207001. Epub 2011 May 20.


The tetragonal heavy-fermion compound CeCu₂Si₂ exhibits a superconducting ground state (S type, T(c) = 0.67 K) close to a magnetic instability. Here, we present angle-resolved resistivity measurements of the upper critical field H(c2). In-plane rotation of S-type CeCu₂Si₂ single crystals reveals a fourfold oscillation of H(c2). An extended weak-coupling BCS model for a d-wave symmetry including strong Pauli-limiting effects confirms the aforementioned angular dependence and points towards d(xy) symmetry of the order parameter.